From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bill Davidsen Subject: Re: strange test results Date: Tue, 20 Mar 2007 11:14:39 -0400 Message-ID: <45FFFA5F.5020805@tmr.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Tomka Gergely Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids Tomka Gergely wrote: > Hi! > > I am running tests on our new test device. The device has 2x2 core Xeon, > intel 5000 chipset, two 3ware sata raid card on pcie, and 15 sata2 disks, > running debian etch. More info at the bottom. > > The first phase of the test is probing various raid levels. So i > configured the cards to 15 JBOD disks, and hacked together a testing > script. The script builds raid arrays, waits for sync, and then runs this > command: > > iozone -eM -s 4g -r 1024 -i0 -i1 -i2 -i8 -t16 -+u > > The graphs of the results here: > > http://gergely.tomka.hu/dt/index.html > > And i have a lots of questions. > > http://gergely.tomka.hu/dt/1.html > > This graph is crazy, like thunderbolts. But the raid50 is generally slower > than raid5. Why? > > http://gergely.tomka.hu/dt/3.html > > This is the only graph i can explain :) > > http://gergely.tomka.hu/dt/4.html > > With random readers, why raid0 slowing down? And why raid10 faster than > raid0? Because with two copies of the data there is a better chance that one copy will be on a drive which is less busy, and/or has a shorter seek to position the heads. If you want to verify this you could create a RAID-1 with three (or more) copies and run readers against that. BTW: that's the only one of your questions I could answer quickly. -- bill davidsen CTO TMR Associates, Inc Doing interesting things with small computers since 1979